East-Central and Southeast Iowa Crop
Information

The continuous thunderstorms have not only delayed planting this
spring, but may now result in having to change cropping plans or even abandon
planting a crop. Most of the corn has been planted, but many farmers do have a
field or two left to plant, especially in the south. Although decent yields can
be obtained with corn planted as late as June 10-15, the risk and yield
variability increases substantially with corn planted in mid June. On average
the yield potential is about 68% of what the corn could have yielded if it had
been planted in early May. If planting is delayed beyond June 10-15, it would
be best to switch to soybeans as long as any applied herbicides will allow it.
If any atrazine has been applied, soybeans should not
be planted. Even though soybeans often can tolerate some atrazine,
it is not legal to plant soybeans into soil with atrazine
and would be very risky. Mike Owen has an article regarding rotational
intervals for planting soybeans after corn herbicides in the ICM News at http://www.extension.iastate.edu/CropNews/2008/0531MikeOwen2.htm.

Because of the poor planting and growing conditions, there are
corn fields that could benefit from re-planting, but if the rains continue,
this becomes less of an option. It would now take corn stands of less than
12,000 plants per acre to justify re-planting. It would be best to use very
early corn hybrids (more than 10 days earlier than full season) when planting
after June 10, if you can find the seed. Fuller season hybrids will still have
greater yield potential than early maturing hybrids, but the risk would be high
that they would not reach maturity before frost and result in poor quality, wet
grain. The Corn Planting Guide can help in making decisions: http://www.extension.iastate.edu/Publications/PM1885.pdf.

Soybean

I’m finally starting to see some emerged soybean fields, but I’m guessing about
a third of the soybeans are yet to be planted. Soybeans do respond more to
narrow rows the later that planting is delayed, so using a drill or planting in
15” rows would be preferable to the 30” rows it that is an option. Seeding
rates do not need to be increased with late planting. Good soybean yields can
be obtained with mid-June planting, especially in southern Iowa, but as with corn the yield variability
becomes greater the greater the delay in planting. On average, soybeans yield
about 82% of the full yield when planted in mid-June in southern Iowa, but only about 60% in central and northern Iowa. Some are also
making replant decisions now for soybeans. Soybean is less sensitive to population than
corn. Use the following tables to help in making re-plant decisions.

I
haven’t thought much about the prevented planting insurance options since 1995,
but unfortunately there are farmers faced with these choices again. A document
that goes into the details is available at http://www.extension.iastate.edu/agdm/crops/pdf/a1-57.pdf.
In short, from
June 1st through June 25th the reduction in insurance is
1%/day for corn. The same is true for soybeans from June 16th to
July 10. Prevented planting and crops planted after the late planting period
ends (June 25 for corn and July 10 for soybeans) are at 60% of the original
guarantee for timely planted acres. If an election was made when the
policy was written to change the 60% to 65% or 70% then that number would
prevail.

Nitrogen
Losses

With the excess rain
we have likely experienced nitrogen losses in many fields through leaching or denitrification. It’s not too late to be pulling soil
samples to test for nitrate. The cool weather this spring would have delayed
the nitrification of ammonium to nitrate, which will likely be occurring now at
a much more rapid rate with these warmer temperatures. Soil nitrate samples
should be pulled to a one foot depth when the corn is 6-12” tall. A minimum of
16 cores should be pulled per sample (24 if there are zones of high N
concentration from anhydrous or manure applications). With the excess rain it
is likely that some nitrate has leached below the one foot depth, but may still
be available for the corn. Because of this it is recommended to reduce the
critical nitrate level from 25 ppm to 20-22 ppm. To calculate nitrogen fertilizer needs you subtract
the nitrate result from the lab from the critical value and multiply by 8. On
soybean ground without manure, if the test reads 15 ppm
and 20 ppm is the critical value chosen, the
recommended nitrogen rate would be 40 lb/A [(20-15)X8]. Some results have been
on the low side this spring, which may be due to ammonium not being mineralized
yet and/or nitrate being lost. For more information on how to pull soil samples
for the late spring soil nitrate test see http://www.extension.iastate.edu/Publications/PM1714.pdf.

PESTS

Corn

Continue
scouting for cutworms

There have been fields sprayed for cutworms this week in the area. The problems
are most likely to be found where there were weeds in the field that attracted
the cutworm moths, but any field can be hit. Continue scouting until the corn
is at V5 (five leaf collars visible).

Seedling
diseases

The cool wet weather has increased problems with damping off from pythium and other seedling diseases. Hopefully the warmer
weather we are seeing now will help to reduce these problems.

Soybean

Asian
Soybean Rust

Some good news is that according to X.B. Yang’s model, there is
little chance of any rust spores reaching Iowa in the next few weeks. Although rust
has been found in Texas,
dry weather there should help prevent its spread. You can see the latest of
what is being found in the south at http://sbrusa.net/cgi-bin/sbr/public.cgi.

FOR YOUR CALENDAR

SPRING FIELD DAY
& SPECIAL SESSION FOR CCAs

SE IA RESEARCH FARM –
CRAWFORDSVILLE

JUNE 26

Certified Crop
Advisors can obtain 5 hours of credit (including 2 hours of soil and water) by
attending a special session in the morning followed by a controlled drainage
field day and the afternoon field tour at the ISU SE Iowa Research &
Demonstration Farm near Crawfordsville on June 26. There is a $50 fee for
credit ($70 after June 24). You can pay at the door (check or cash), but please
call the JohnsonCounty Extension office at 319-337-2145
or send me an e-mail note by June 24 if you plan to attend.

The
controlled drainage field day and afternoon tour are free to the public (if not
obtaining credit). The lunch at noon is courtesy of Qualisoy.